Identifying the Alkali Reactivity of Concrete Aggregates--Tests on Autoclaved Concrete Samples

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Title: Identifying the Alkali Reactivity of Concrete Aggregates--Tests on Autoclaved Concrete Samples

Author(s): Salil K. Roy, Poh Kong Beng and Derek 0. Northwood

Publication: Special Publication

Volume: 172

Issue:

Appears on pages(s): 193-208

Keywords: Alkali-silica reactions; dynamic modulus of elasticity; ultrasonic tests

Date: 12/1/1999

Abstract:
Concrete prisms (40 x 40 x 160 mm) were made with crushed aggregate, non-reactive sand, portland cement with added alkali (NaOH) content (2.5%’ by mass), and water in proportion (by mass) of 1: 1: 1:0.5. The prisms were demolded after 24 hours, cured in water at room temperature for another 24 hours, then boiled under water at a constant pressure (0.15 Mpa) and temperature of 111°C in an autoclave for 2 hours, cooled to room temperature and examined for presence of cracks and changes (before and after boiling) in ultrasonic pulse velocity as well as dynamic Young’s modulus. Conditions for a suspect aggregate to be innocuous could be established from measurements made on aggregates collected from twelve quarries in Singapore, and on a sample of one of these aggregates mixed with an opal from Indonesia. Results obtained by this method are found to agree with those obtained by each of the three ASTM methods (Petrographic Examination (C 229-85) Chemical Method (C 295- 85) and Mortar Bar Expansion Test (C 227-81).